Volume Stabilizer

Discussion in 'Playback Devices' started by Rick Chaisse, May 24, 2006.

  1. Rick Chaisse

    Rick Chaisse Extra

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    I have a restaurant sound system where the customer's music source is an ipod. the volume levels of the songs vary considerably.

    Does anyone know of a volume stabilizer that will work ?

    Thanks
     
  2. Jerome Grate

    Jerome Grate Cinematographer

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    Do you mean each customer can use their individual Ipods to listen to music or is the ipod your own? If the only ipod is your own then maybe the installation of the volume controller from Apple should work.
     
  3. Leo Kerr

    Leo Kerr Screenwriter

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    Symetrix, among others, make compressors. Many of these will also "duck" for paging over music. Some of them also link to a mic or two throughout the listening area so that as the noise-floor of the restaurant rises and falls, the audio playback also rises and falls (within certain limits.)

    Take a look at, for example, the Symetrix 322 DSP engine.

    http://www.symetrixaudio.com/index.p...1=33&Show2=322

    Leo Kerr
     
  4. chris_everett

    chris_everett Second Unit

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    Yep, you need a compressor (we are talking about dynamic range compression here, not data compression) I would recommend you call the people at www.sweetwater.com. They are very helpful, and can recommend something for your application.
     
  5. Dick Knisely

    Dick Knisely Second Unit

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    uh, guys, that's true if the problem he has is volume level variance within a track -- compressing out the dynamics helps there. But if the problem he's referring to is variance in volume level of one track to another, a dynamic compression scheme isn't the answer, is it? Doesn't he need to run the tracks through a software application that applies a gain control/leveling?
     
  6. Leo Kerr

    Leo Kerr Screenwriter

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    a real-time dynamics compressor is only looking at the signal at the instant, relative to, say, the past few seconds. It has absolute target levels set, based upon an input voltage.

    For example, if the input signal is 0 - 1v. Imagine these are settings on the compressor. The units aren't the ones that you'll see on the controls, but this is sort of how they work...

    "Gate" set to 0.05v
    Threshold at 0.8v
    Compression rate: 2:1
    Peak Stop 0.9v
    "Duck" set to -0.3v
    Ramp set to 0.05v/ms
    Integration time: 20ms

    So. Now the translation:
    Gate: means if the signal is below 0.05v, mute the input entirely.
    Threshold. Once the input voltage reaches 0.8v, start compressing.
    With the rate of 2:1, input 0.9v = output 0.85v
    Peak stop means that anything above 0.9v gets limited to 0.9v.
    Duck of -0.3v means when you turn on the mic that goes over the music, it drops the music level by 0.3v.
    Ramp: when the compressor begins to work, or release, it applies its voltage regulation at the certain rate. Often times, the attack and release can be set seperately; generally, the attack is set fairly fast, and the release moderately slow.
    Integration time: This tells the compressor to look at the RMS voltage level over, in this case, 20ms. So rather than pumping with every slightest transient, as the RMS signal level over that interval rises above the 0.8v, then it starts to apply.

    Many of these boxes are entirely analog boxes, operating entirely in the real-time domain. And, if one track is overly high, it will be "compressed" compared to the track that's generally softer.

    Some compressors will also have a "boost" phase, where if the RMS voltage is below a certain threshold, it will pump the level up, as well.

    Leo
     
  7. chris_everett

    chris_everett Second Unit

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    You can run everything through some software and get levels where you want, but that's rather time consuming. A compressor is ideal for this application (background music in a restraunt) It will tamp down the loud portions, and can bring up the lower ones (via a knob usually labeled "make-up gain") It does take some time to get a compressor set up correctly.
     
  8. Richard Travale

    Richard Travale Producer

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    I wanted to resurrect this thread.
    I am curious what program is out there that would do this?
    I just bought an FM transmitter for my iPod to use in the car and I am finding that the songs with lower gain are extremely noticeable using the transmitter as opposed to just using the headphones.
     
  9. ChristopherDAC

    ChristopherDAC Producer

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    As a first step, you might try normalising the track volume, using a wave-editor application [if you don't have one, there are some free ones ; I think there is even one bundled into EAC, the CD-ripping program].

    After that you can look at dynamic compression ; I know the NERO wave editor lets you create a transfer curve. Of course, even if your wave editor can import and export compressed files, it's better to work with an actual .WAV PCM audio file, to avoid messy results.
     
  10. Leo Kerr

    Leo Kerr Screenwriter

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    Cool Edit now marketed as Adobe Audition has excellent dynamic compression features.

    I'm sure there are others, likely cheaper versions, too.

    Leo
     

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